Major histcompatibility complex (MHC) class I molecules present intracellular pathogen-derived peptides to T-cells, which become activated upon engagement of clonotypis alphabeta T-cell antigen receptors (TCRs) and of costimulatory receptors. Distant homologs of MHC class I molecules have altered functions and interact with different receptors and T-cell subsets. Among these are human MICA andMICB, which are cell stress-inducible surface molecules that are not associated with antigenic peptide or nonpeptide ligands. They have a limited expression in intestinal epithelium and epithelial tumors, can be potently induced in virus-infected cells, and are recognized as self-antigens by a subset of T-cells with gammadelta TCRs that is frequently enriched in epithelial sites. In addition, MICA/B function as ligands for an activating recepotr, NKG2D, which is broadly expressed on lymphocyte subsets. Engagement of NKG2Dcan trigger natural killer (NK) cells and augment responsesby antigen-specific CD8+ alphabeta T-cells and gammadelta T-cells. The here proposed research aims at advancingknowledge of this immunological system that may be capableof mobilizing diverse effector cells against tumor andvirus-infected cells. Studies planned under Specific Aim I will define the molecular mechanisms underlying the stress-inducible expression of the MICA/B genes. Transcriptionalinduction will be measured, relevant transcription factorsidentified, and their binding to predictable sites within adefined promoter context determined. Studies under Specific Aim II are designed to demonstrate interactions of MICA/Bwith gammadelta TCRs and to investigate how variable gammaand delta chains contribute to TCR specificity. Furthergoals are to quantify the subset of gammadelta T-cellsspecific for MICA/B and to determine the role of NKG2D inactivation. Studies under Specific Aims III will investigate the induction of MICA/B in cells infected by cytomegalovirus and the function of NKG2D in promoting virus-specific CD8+ alphabeta T-cell responses. This and additional experimental systems have been chosen to demonstrate that NKG2D can costimulate TCR-mediated T-cell activation.